The present invention relates to Group IVB (titanium, hafnium, zirconium) boride based articles, cutting tools and their densification techniques. It is especially related to titanium diboride based cutting tools and their use to machine Group IVB metals and alloys, especially titanium and its alloys.
It was recognized as early as 1955 that "machining of titanium and its alloys would always be a problem, no matter what techniques are employed to transform this metal into chips," (Siekmann H. J. Tool Engng, January 1955, Vol. 34, Pages 78-82).
Over approximately the past forty years, commercial machining technology for most workpiece materials has advanced significantly. Ceramic, cermet and ceramic coated cutting tools have been developed and commercialized which have significantly improved productivity in machining of steels, cast irons and superalloys. However, during that same time period, progress in the field of machining titanium alloys has been minor. The commercial cutting tool materials of choice for most titanium machining applications remain high speed tool steels and an uncoated, approximately 6 weight percent cobalt cemented tungsten carbide, such as Kennametal K313 cemented carbide grade. Where coated cemented carbide tools (e.g., Kennametal, KC720 and KC730 grades) have been applied to titanium alloy machining, they have met with only limited success. The use of uncoated cemented carbides to machine titanium based metallic materials has greatly limited productivity advances in the machining of these materials, since uncoated carbides are limited in most commercial applications to speeds of 250 surface feet/minute or less when machining titanium alloys (see Dearnley et al., "Evaluation of Principal Wear Mechanisms of Cemented Carbides and Ceramics used for Machining Titanium Alloy IMI318," Materials Science and Technology, January 1986, Vol. 2, Pages 47-58; Dearnley et al., "Wear Mechanisms of Cemented Carbides and Ceramics used for Machining Titanium," High Tech Ceramics, ed. by P. Vincenzini, Elsevier Sci. Publ. (1987) Pages 2699-2712; Metals Handbook, Ninth Edition, Vol. 16, "Machining," (1989), Pages 844-857; Marchado et al., "Machining of Titanium and Its Alloys --A Review," Proc. Instn. Mech. Engrs., Vol. 204 (1990) Pages 53-60; and "Kennametal Tools, Tooling Systems and Services for the Global Metalworking Industry," Catalogue No. A90-41(150)E1, (1991) Page 274.
Kennametal, KC, K313, KC720 and KC730 are trademarks of Kennametal Inc., of Latrobe, Pennsylvania, for its cutting tool grades.
The machining speed used when machining titanium alloys with uncoated cemented carbide tools may be increased to 500 to 1000 surface feet/minute, through the use of a high pressure coolant machining system (e.g., U.S. Pat. No. 4,621,547). These systems are expensive, difficult to integrate into existing machine tools, and require a significant amount of maintenance. Their application in titanium alloy machining has, therefore, been limited.
Clearly, there has thus been an unfulfilled long-felt need for improved cutting tool materials, and improved methods for machining titanium based metallic materials.